add --partial option

README.md

@@ -107,15 +107,17 @@ Then, update your hash key to include a checksum of that file:
 ```yaml
 - restore_cache:
     key:
-      app-node_modules-v1-{{ checksum "yarn.lock" }}-{{ checksum "patches.hash" }}
+      app-node_modules-v1-{{ checksum "yarn.lock" }}-{{ checksum "patches.hash"
+      }}
 ```
 
 As well as the save_cache
 
 ```yaml
 - save_cache:
     key:
-      app-node_modules-v1-{{ checksum "yarn.lock" }}-{{ checksum "patches.hash" }}
+      app-node_modules-v1-{{ checksum "yarn.lock" }}-{{ checksum "patches.hash"
+      }}
     paths:
       - ./node_modules
 ```
@@ -342,6 +344,21 @@ If you deleted one of the patch files other than the last one, you don't need to
 update the sequence numbers in the successive patch file names, but you might
 want to do so to keep things tidy.
 
+#### Partially applying a broken patch file
+
+Normally patch application is atomic per patch file. i.e. if a patch file
+contains an error anywhere then none of the changes in the patch file will be
+applied and saved to disk.
+
+This can be problematic if you have a patch with many changes and you want to
+keep some of them and update others.
+
+In this case you can use the `--partial` option. Patch-package will apply as
+many of the changes as it can and then leave it to you to fix the rest.
+
+Any errors encountered will be written to a file `./patch-package-errors.log` to
+help you keep track of what needs fixing.
+
 ## Benefits of patching over forking
 
 - Sometimes forks need extra build steps, e.g. with react-native for Android.

integration-tests/partial-apply/__snapshots__/partial-apply.test.ts.snap

@@ -0,0 +1,50 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Test partial-apply: 00: patch-package fails when one of the patches in the sequence fails 1`] = `
+"SNAPSHOT: patch-package fails when one of the patches in the sequence fails
+patch-package 0.0.0
+Applying patches...
+left-pad@1.3.0 (1 hello) ✔
+
+⛔ ERROR
+
+Failed to apply patch file left-pad+1.3.0+002+world.patch.
+
+If this patch file is no longer useful, delete it and run
+
+  patch-package
+
+To partially apply the patch (if possible) and output a log of errors to fix, run
+
+  patch-package --partial
+
+After which you should make any required changes inside node_modules/left-pad, and finally run
+
+  patch-package left-pad
+
+to update the patch file.
+
+END SNAPSHOT"
+`;
+
+exports[`Test partial-apply: 01: patch-package --partial saves a log 1`] = `
+"SNAPSHOT: patch-package --partial saves a log
+patch-package 0.0.0
+Applying patches...
+left-pad@1.3.0 (1 hello) ✔
+Saving errors to ./patch-package-errors.log
+patch-package-errors.log
+Cannot apply hunk 0 for file node_modules/left-pad/index.js
+\`\`\`diff
+@@ -3,7 +3,7 @@
+      * and/or modify it under the terms of the Do What The Fuck You Want
+      * To Public License, Version 2, as published by Sam Hocevar. See
+      * http://www.wtfpl.net/ for more details. */
+-'use oops';
++'use world';
+ module.exports = leftPad;
+ 
+ var cache = [
+\`\`\`
+END SNAPSHOT"
+`;

integration-tests/partial-apply/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "partial-apply",
+  "version": "1.0.0",
+  "description": "integration test for patch-package",
+  "main": "index.js",
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "left-pad": "^1.3.0"
+  }
+}

integration-tests/partial-apply/partial-apply.sh

@@ -0,0 +1,26 @@
+#!/bin/bash
+# make sure errors stop the script
+set -e
+
+npm install
+
+echo "add patch-package"
+npm add $1
+
+function patch-package {
+  ./node_modules/.bin/patch-package "$@"
+}
+
+echo "SNAPSHOT: patch-package fails when one of the patches in the sequence fails"
+if patch-package
+then
+  exit 1
+fi
+echo "END SNAPSHOT"
+
+
+echo "SNAPSHOT: patch-package --partial saves a log"
+patch-package --partial
+echo 'patch-package-errors.log'
+cat patch-package-errors.log
+echo "END SNAPSHOT"

integration-tests/partial-apply/partial-apply.test.ts

@@ -0,0 +1,5 @@
+import { runIntegrationTest } from "../runIntegrationTest"
+runIntegrationTest({
+  projectName: "partial-apply",
+  shouldProduceSnapshots: true,
+})

integration-tests/partial-apply/patches/left-pad+1.3.0+001+hello.patch

@@ -0,0 +1,13 @@
+diff --git a/node_modules/left-pad/index.js b/node_modules/left-pad/index.js
+index e90aec3..1a2ec5f 100644
+--- a/node_modules/left-pad/index.js
++++ b/node_modules/left-pad/index.js
+@@ -3,7 +3,7 @@
+      * and/or modify it under the terms of the Do What The Fuck You Want
+      * To Public License, Version 2, as published by Sam Hocevar. See
+      * http://www.wtfpl.net/ for more details. */
+-'use strict';
++'use hello';
+ module.exports = leftPad;
+
+ var cache = [

integration-tests/partial-apply/patches/left-pad+1.3.0+002+world.patch

@@ -0,0 +1,13 @@
+diff --git a/node_modules/left-pad/index.js b/node_modules/left-pad/index.js
+index 1a2ec5f..5aa41be 100644
+--- a/node_modules/left-pad/index.js
++++ b/node_modules/left-pad/index.js
+@@ -3,7 +3,7 @@
+      * and/or modify it under the terms of the Do What The Fuck You Want
+      * To Public License, Version 2, as published by Sam Hocevar. See
+      * http://www.wtfpl.net/ for more details. */
+-'use oops';
++'use world';
+ module.exports = leftPad;
+
+ var cache = [

integration-tests/partial-apply/patches/left-pad+1.3.0+003+goodbye.patch

@@ -0,0 +1,13 @@
+diff --git a/node_modules/left-pad/index.js b/node_modules/left-pad/index.js
+index 5aa41be..5ee751b 100644
+--- a/node_modules/left-pad/index.js
++++ b/node_modules/left-pad/index.js
+@@ -3,7 +3,7 @@
+      * and/or modify it under the terms of the Do What The Fuck You Want
+      * To Public License, Version 2, as published by Sam Hocevar. See
+      * http://www.wtfpl.net/ for more details. */
+-'use world';
++'goodbye world';
+ module.exports = leftPad;
+
+ var cache = [

property-based-tests/executeTestCase.ts

@@ -132,7 +132,7 @@ export function executeTestCase(testCase: TestCase) {
     fs.setWorkingFiles({ ...testCase.cleanFiles })
     reportingFailures(() => {
       const effects = parsePatchFile(patchFileContents)
-      executeEffects(effects, { dryRun: false })
+      executeEffects(effects, { dryRun: false, bestEffort: false })
       expect(fs.getWorkingFiles()).toEqual(testCase.modifiedFiles)
     })
   })
@@ -141,7 +141,7 @@ export function executeTestCase(testCase: TestCase) {
     fs.setWorkingFiles({ ...testCase.modifiedFiles })
     reportingFailures(() => {
       const effects = reversePatch(parsePatchFile(patchFileContents))
-      executeEffects(effects, { dryRun: false })
+      executeEffects(effects, { dryRun: false, bestEffort: false })
       expect(fs.getWorkingFiles()).toEqual(testCase.cleanFiles)
     })
   })

src/applyPatches.ts

@@ -1,4 +1,5 @@
 import chalk from "chalk"
+import { writeFileSync } from "fs"
 import { existsSync } from "fs-extra"
 import { posix } from "path"
 import semver from "semver"
@@ -96,12 +97,14 @@ export function applyPatchesForApp({
   patchDir,
   shouldExitWithError,
   shouldExitWithWarning,
+  bestEffort,
 }: {
   appPath: string
   reverse: boolean
   patchDir: string
   shouldExitWithError: boolean
   shouldExitWithWarning: boolean
+  bestEffort: boolean
 }): void {
   const patchesDirectory = join(appPath, patchDir)
   const groupedPatches = getGroupedPatches(patchesDirectory)
@@ -124,6 +127,7 @@ export function applyPatchesForApp({
       reverse,
       warnings,
       errors,
+      bestEffort,
     })
   }
 
@@ -165,13 +169,15 @@ export function applyPatchesForPackage({
   reverse,
   warnings,
   errors,
+  bestEffort,
 }: {
   patches: PatchedPackageDetails[]
   appPath: string
   patchDir: string
   reverse: boolean
   warnings: string[]
   errors: string[]
+  bestEffort: boolean
 }) {
   const pathSpecifier = patches[0].pathSpecifier
   const state = patches.length > 1 ? getPatchApplicationState(patches[0]) : null
@@ -257,6 +263,7 @@ export function applyPatchesForPackage({
           patchDetails,
           patchDir,
           cwd: process.cwd(),
+          bestEffort,
         })
       ) {
         appliedPatches.push(patchDetails)
@@ -397,12 +404,14 @@ export function applyPatch({
   patchDetails,
   patchDir,
   cwd,
+  bestEffort,
 }: {
   patchFilePath: string
   reverse: boolean
   patchDetails: PackageDetails
   patchDir: string
   cwd: string
+  bestEffort: boolean
 }): boolean {
   const patch = readPatch({
     patchFilePath,
@@ -412,14 +421,26 @@ export function applyPatch({
 
   const forward = reverse ? reversePatch(patch) : patch
   try {
-    executeEffects(forward, { dryRun: true, cwd })
-    executeEffects(forward, { dryRun: false, cwd })
+    if (!bestEffort) {
+      executeEffects(forward, { dryRun: true, cwd, bestEffort: false })
+    }
+    const errors: string[] | undefined = bestEffort ? [] : undefined
+    executeEffects(forward, { dryRun: false, cwd, bestEffort, errors })
+    if (errors?.length) {
+      console.log(
+        "Saving errors to",
+        chalk.cyan.bold("./patch-package-errors.log"),
+      )
+      writeFileSync("patch-package-errors.log", errors.join("\n\n"))
+      process.exit(0)
+    }
   } catch (e) {
     try {
       const backward = reverse ? patch : reversePatch(patch)
       executeEffects(backward, {
         dryRun: true,
         cwd,
+        bestEffort: false,
       })
     } catch (e) {
       return false

src/index.ts

@@ -24,6 +24,7 @@ const argv = minimist(process.argv.slice(2), {
     "error-on-fail",
     "error-on-warn",
     "create-issue",
+    "partial",
     "",
   ],
   string: ["patch-dir", "append", "rebase"],
@@ -120,6 +121,7 @@ if (argv.version || argv.v) {
       patchDir,
       shouldExitWithError,
       shouldExitWithWarning,
+      bestEffort: argv.partial,
     })
   }
 }

src/makePatch.ts

@@ -214,7 +214,7 @@ export function makePatch({
         })
       } catch (e) {
         // try again while ignoring scripts in case the script depends on
-        // an implicit context which we havn't reproduced
+        // an implicit context which we haven't reproduced
         spawnSafeSync(
           `yarn`,
           ["install", "--ignore-engines", "--ignore-scripts"],
@@ -238,7 +238,7 @@ export function makePatch({
         })
       } catch (e) {
         // try again while ignoring scripts in case the script depends on
-        // an implicit context which we havn't reproduced
+        // an implicit context which we haven't reproduced
         spawnSafeSync(`npm`, ["i", "--ignore-scripts", "--force"], {
           cwd: tmpRepoNpmRoot,
           stdio: "ignore",
@@ -278,6 +278,7 @@ export function makePatch({
           patchFilePath: join(appPath, patchDir, patchDetails.patchFilename),
           reverse: false,
           cwd: tmpRepo.name,
+          bestEffort: false,
         })
       ) {
         // TODO: add better error message once --rebase is implemented
@@ -498,6 +499,7 @@ export function makePatch({
               patchFilePath,
               reverse: false,
               cwd: process.cwd(),
+              bestEffort: false,
             })
           ) {
             didFailWhileFinishingRebase = true
@@ -587,10 +589,14 @@ Failed to apply patch file ${chalk.bold(patchDetails.patchFilename)}.
 If this patch file is no longer useful, delete it and run
 
   ${chalk.bold(`patch-package`)}
-  
-Otherwise you should open ${
+
+To partially apply the patch (if possible) and output a log of errors to fix, run
+
+  ${chalk.bold(`patch-package --partial`)}
+
+After which you should make any required changes inside ${
     patchDetails.path
-  }, manually apply the changes from the patch file, and run
+  }, and finally run
 
   ${chalk.bold(`patch-package ${patchDetails.pathSpecifier}`)}